CAS REGISTRY®
Access the CAS REGISTRY, the world’s most trusted source for accurate chemical substance information. Whether you’re a scientist, manufacturer, regulator, or data scientist, our comprehensive collection provides reliable data to support your work.
Look up a CAS Registry Number®
![A digital card displaying information about the element nitrogen from the periodic table. It includes the atomic number 7, atomic mass range [14.00643, 14.00728], symbol 'N', and electron configuration [He]2s²2p³. A blue box with white text shows the CAS registry number 7727-37-9.](https://cdn.prod.website-files.com/650861f00f97fe8153979335/68557701f77e4a8e679046f9_d838e484db6befacc157d5154308fe6d_what-is-reg-number.svg)
What is a CAS Registry Number®?
Chemical compounds are described in many ways, including molecular formulas, chemical structures, generic, systematic, common, and trade names. This lack of clarity can cause frustration, delays, and even safety concerns.
A CAS Registry Number (CAS RN®) is a unique and unambiguous identifier for a specific substance that allows clear communication and, with the help of CAS scientists, links together all available data and research about that substance. Governmental agencies rely on CAS Registry Numbers for substance identification in regulatory applications because they are unique, easily validated, and internationally recognized.
Why are CAS Registry Numbers (CAS RNs®) used?
CAS Registry Numbers set the standard for identifying chemical substances since 1965.
- Each CAS RN uniquely identifies a chemical substance, avoiding confusion from multiple names.
- CAS RNs allow quick access to detailed chemical information in CAS solutions, including our open community resource, CAS Common Chemistry™.
- CAS RNs are a global standard, making international communication and collaboration easier.
Looking for CAS Registry Numbers or CA Index Names for known substances?
For common and frequently regulated chemicals, you can use CAS Common Chemistry, an open community resource with nearly 500,000 chemical substances from CAS REGISTRY.
If you’re looking for a more unique substance, simply complete and submit a CAS Registry Lookup service order form and receive results within 24 hours (excluding weekends and holidays).
What is the difference between the CAS REGISTRY and a CAS Registry Number?
CAS REGISTRY is the database of disclosed chemical substances curated from scientific literature and other sources. It contains over 290 million substances and is continuously enhanced with new substances and the most up-to-date information for substances in the collection.
CAS Registry Numbers (CAS RNs) are the unique numeric identifiers assigned to chemical substances within the CAS REGISTRY. A CAS RN designates only one substance, ensuring precise identification. They allow for clarity in research across regions and languages and allow CAS databases and solutions to link a wealth of information about specific substances.
![A digital interface displaying the chemical structure of a compound with CAS Registry Number 152342-19-3. Tabs labeled 'Reference (1)', 'Reactions (1)', and 'Supplier (1)' are visible. The compound's formula is C₂₂H₂₃N₃O, and its name is 4H-Pyrrolo[1,2-b]pyridazin-4-acetamide, N-butyl-2-phenyl-.](https://cdn.prod.website-files.com/650861f00f97fe8153979335/685577013343c6ae0554bf34_a204913df55d0aa9ac776a1c847272bf_registry-services-chemical-structure-cas-152342-19-3.avif)
What does a CAS Registry Number look like?
CAS Registry ServicesSM
Explore our services to obtain CAS Registry Numbers and/or CA Index Names to include in your regulatory submissions, or consult with chemists for expert substance information.